The BBC and Master Computer Public Domain Library

Floating-point Sign

Submitted by Steve Fewell

Routine: Asign
Name: Return the sign of the number in the FWA
Starting Address: &A3F2
Entry criteria: None
Exit: A = 0 if the FWA contains zero, A = 1 if the FWA contains a positive number, A = -1 if the FWA contains a negative number.

Description:
Load A with FWA Mantissa Byte 1, OR this value with the other Mantissa bytes (byte 2 to byte 5), If the result is zero, then the whole of the FWA Mantissa is zero, this signifies that the number in the FWA is zero, if this is so, then store zero in the FWA Sign, FWA Exponent and FWA overflow bytes and return with A = 0.

Otherwise, Load A with the FWA Sign Byte, if it isn't zero, then the FWA is negative, and the top bit of the sign byte must be set. So exit with A containing the sign byte (-1).

Otherwise, increment A (to get a result of 1) and return.

Disassembly for the Floating-point Sign routine